[llvm] [GlobalISel] Combine G_MERGE_VALUES of x and undef (PR #113616)

[Thorsten Schütt via llvm-commits]

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@@ -0,0 +1,57 @@
+//===- CombinerHelperArtifacts.cpp-----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements CombinerHelper for legalization artifacts.
+//
+//===----------------------------------------------------------------------===//
+//
+// G_MERGE_VALUES
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/CodeGen/GlobalISel/CombinerHelper.h"
+#include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
+#include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
+#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/LowLevelTypeUtils.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetOpcodes.h"
+#include "llvm/Support/Casting.h"
+
+#define DEBUG_TYPE "gi-combiner"
+
+using namespace llvm;
+
+bool CombinerHelper::matchMergeXAndUndef(const MachineInstr &MI,
+                                         BuildFnTy &MatchInfo) {
+  const GMerge *Merge = cast<GMerge>(&MI);
+
+  Register Dst = Merge->getReg(0);
+  Register Undef = Merge->getSourceReg(1);
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tschuett wrote:

I am wondering what guarantees the pattern gives. Are there exactly two sources? Would it also fit G_MERGE_VALUES with 10^6 sources?

https://github.com/llvm/llvm-project/pull/113616